Jennifer Little BSc Hons MSc RNutr PgCert
Independent Equine Nutritionist
Importance of the hindgut
The horse has an unusual digestive system, with digestion in the foregut being driven by chemical and enzyme reactions. Whereas digestion in the hindgut is driven by the action of microbes, which include bacteria and protozoa. Collectively these microbes are known as the gut biome, or microbiota.
Over half the maintenance energy requirement in the horse is produced from the action of these microbes . These microbes are responsible for far more than just energy production, they directly and indirectly interact with the cells of the digestive tract and are involved in other functions such as producing certain vitamins, and influencing both systemic inflammation and immune regulation .
Challenges to hindgut health
Multiple factors can challenge and alter the sensitive balance of the microbiota. These include, but are not limited to;
– Dietary changes
– Management changes
– Group dynamic changes
– Certain medications, such as antibiotics
Changes in the microbiota can result in diseases such as diarrhoea, colic, Equine Gastric Ulcer Syndrome (EGUS), colitis, laminitis, equine metabolic syndrome, increased infection rates as well as poor body condition, slowed tissue healing and poor performance or growth rates .
Development of the gut micro-biome in the foal
It is critical for the immediate and long term health that a newborn foal is able to acquire a beneficial and balanced population of micro-organisms to colonise it’s own microbiota early. The role of the dam is pivatol to this process, with microbial transmission occurring due to the repeated interaction between foal and dam . In the new born foal the microbiota is highly unstable and susceptible to rapid changes . One behaviour that has can rapidly change the composition of the microbiota in foals to one more similar to that of an adult horse is coprophagia (the act of eating horse faeces), this normally occurs within the first week of age [3;4]. The foals microbiota continues to evolve and once over the age of 2 months is should have established the bacteria required for the digestion and fermentation of fibre sources typically found in an adult horses diet .
Weaning – The Perfect Storm
In the time for weaning the microbiota should have just matured to the point of having the high potential for the digestion of dietary compounds offered to young horses . Unfortunately the act of weaning threatens to challenge this newly achieved microbiota maturity status. Of the 8 challenges to hindgut health listed above, 1-7 commonly collide into a perfect storm at weaning. The stress induced by weaning causes the production of stress hormones, to which the gut responds by synthesising cytokines, neurotransmitters and other stress hormones. These reduce the beneficial gut micro-biome activity and diversity, and may even promote the growth of intestinal pathogens [6:7]. Significant changes to the microbiota can occur within just three days after weaning . These changes have been associated with welfare deterioration through changes in behaviours, including increased fight and flight responses [1;9]. This behavioural response to weaning stress can increase the risk of injuries and therefore it can also increase the likelihood that antibiotics may be required, which is an additional challenge for the hindgut micro-biome.
It can be a common practise that the time of weaning coincides with the need to transport a weanling. Unfortunately a journey as short as two hours can be sufficient to significantly alter the bacteria found in faeces, and increase the risk of gastro-intestinal disorders [10;11].
Supporting hindgut health at weaning
Supporting a well-balanced microbiota is of vital importance for horse health, especially during periods of challenge . Management strategies such as the early introduction of creep feed and gradual weaning, rather than abrupt weaning, have demonstrated reduced disturbances to the gut microbiota .
A strategy for supporting the overall health of a horse, especially during phases of increased stress, is by supporting the microbiota. This approach has gained significant support and evidence in research over the past 15 years.
One area of the research that shows great promise is the use of pre and pro biotics to modulate the microbiota. Probiotics are the live micro-organisms that have the capacity to colonize the gut and support the diversity and function of the micro-biome. There are several types of yeast, but in relation to the horse, a yeast called Saccharomyces cerevisia is the most frequently used and studied .
The use of this probiotic in horses can increase their fibre digestion, restore gut balance and even increase a horses ability to manage changes [1;14;15]. A mechanism of this yeast is that is scavenges oxygen present within the digestive tract, and in doing so creates an environment more suitable for the beneficial, anaerobic bacteria . The supplementation of Saccharomyces cerevisia has been shown to provide a stress-mitigating response in young horses .
Prebiotics differ from probiotics in that they are not living microorganisms. Instead they provide a food source for the beneficial bacteria, helping to ensure they are sufficient in numbers and have the stability required to maintain hindgut health. Two prebiotics recognised as beneficial in the horse are Fructooligosaccharides (FOS) and Mannanoligosaccharides (MOS).
Supplementation with FOS has been shown to improve the health and welfare of horses . It can be effective in reducing disruptions to the microbiota stressful situations, such as weaning . The inclusion of FOS within a horses diet has even been shown to limit the negative impact of changes to feeds and forages, and to reduce the risk of colic .
The supplementation of MOS is associated with supporting optimal growth rates, health indices, reducing oxidative stress and inflammatory effects . Additionally MOS supplementation has been proven to improve muscle mass, function, recovery and health . It plays an important role in improving horse health and has a positive effect on overall growth rates and performance .
Even with careful management weaning is undoubtedly a challenging and stressful time for a young horse. The effect of weaning stress can directly impact on the health of the bacterial population within the gut, and indirectly impact on the overall health of a young horse. Consideration of the impact of the management of the weaning process, the inclusion of creep feeding and suitable supplementation of pre and pro biotics is a suitable strategy for controlling the impact of weaning stress. Supporting the hindgut Biome may even regulate the weaning stress response .
 Chaucheyras-Durand, F., Sacy, A., Karges, K., Apper, E. 2022 Gastro-Intestinal Microbiota in Equines and its role in health and disease: the black box opens. Microorganisms (10) 2517
 Linderberg,F, Krych,L., Kot,W., Fielden, J., Frokiaer,H., van Galen,G., Nielsen,D.S, Hansen,A.K. 2019 Development of the equine gut microbiota. Sci. Rep. (9) 14427
 Quercia,S., Freccero,F., Castagnetti,C., Soverini,M., Turroni,S., Baigi,E., Rampelli,S., Laci,A., Mariella,J., Chinellato, E. 2019. Early colonisation and temporal dynamics of the gut microbial ecosystems in standardbred foals. Equine Vet. J. (51) 231-237
 Husso, A., Jalanka, J., Alipour, M.J., Huhti, P., Kareskoski, M., Pessa-Morikawa, T., Livanainen, A., Niku, M. 2020. The composition of the perinatal intestinal microbiota in horse. Sci. Rep (10) 441
 La Torre, U.D, Henderson, J.D., Furtado, K.L., Pedroja, M, Elenamarie, O.M., Mora,A., Pechanec, M.Y., Maga, E.A., Mienaltowski, M.J. 2019 Utilising the fecal microbiota to understand foal gut transitions from birth to weaning. PLoS ONE (14) e0216211
 Freestone, P., Lyte, M. 2010 Stress and microbial endocrinology: Prospects for ruminant nutrition. Animals (4) 1248-1257
 Lyte, M. 2013 Microbial endocrinology in the microbiome-gut-brain axis: How bacterial production and utilization of neurochemicals influence behaviour. PLoS Pathog (9) e1003726
 Lyte, M. 2011. Probiotics function mechanistically as delivery vehicles for neuroactive compounds: Microbial endocrinology in the design and use of probiotcs. BioEssays News Rev. Mol.Cell. Dev. Biol (33) 547-581
 Mach, N., Ruet, A., Clark, A., Bars-Cortina, D., Ramayo-Caldas, Y., Crisci, E., Pennarun, S., Dhorne-Pollet, S., Foury, A., Moisan, M.P, 2020 Priming for welfare: gut microbiota is associtated with equitation conditions and behaviour in horse athletes. Sci. Rep. (10) 8311
 Perry, E., Cross, T-W.L, Francis, J.M., Holscher, H.D., Clark, S.D., Swanson, K.S. 2018 Effect of Road transport on equine caecal microbiota. J. Equine Vet. Sci (68) 12-20
 Faubladier, C., Chaucheyras0Durand, F., da Veiga, L., Julliand, V. 2013 Effect of transportation on fecal bacterial communities and fermentative activities in horses: Impact of Saccaromyces cervisiae CNCM I-1077 supplementation. J. Anim. Sci. (91) 1736-1744
 Mach, N., Foury, A., Kittelmann, S., Reigner, F., Moroldo, M., Ballester, M., Esquerre, D., Riviere, J., Salle, G., Gerarad, P. 2017 Effects of weaning methods on gut microbiota composition and horse physiology. Front. Physiol (8) 535
 Perricone, V., Sandrini, S., Irshad, N., Comi, M., Lecchi, C., Savoini, G., & Agazzi, A., 2022 The role of yeast saccharomyces cerevisiae in supporting gut health in horses: An updated review on its effects on digestibility and intestinal faecal microbiota. Animals 12, 3475